When should I use UUID v7 instead of v4?

Use v7 when the identifier is a database primary key or otherwise inserted in time order: its leading timestamp keeps index inserts local. v4 is fully random and is fine when ordering does not matter.

What is the difference between UUID and ULID?

Both are 128-bit identifiers. A ULID is written as 26 Crockford Base32 characters, sorts lexicographically by creation time and is shorter to read; a UUID uses the familiar 36-character hex form with dashes.

Are these identifiers unique?

Yes. v4 and ULID carry 122 and 80 random bits respectively, and v7 carries 74 random bits plus a millisecond timestamp, so collisions are practically impossible at normal application volumes.

Techvoyage

UUID & ULID Generator

Generate UUID v4, time-ordered UUID v7 and ULID identifiers in your browser. Bulk generation with copyable output.

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Generated locally with the Web Crypto API. Nothing leaves your device.

About this tool

UUID v4 is fully random. UUID v7 and ULID both start with a millisecond timestamp, so their values sort by creation time, which keeps database index inserts local. All three are 128-bit identifiers rendered in their standard forms; nothing is sent to a server.

FAQ

When should I use UUID v7 instead of v4?: Use v7 when the identifier is a database primary key or otherwise inserted in time order: its leading timestamp keeps index inserts local. v4 is fully random and is fine when ordering does not matter.
What is the difference between UUID and ULID?: Both are 128-bit identifiers. A ULID is written as 26 Crockford Base32 characters, sorts lexicographically by creation time and is shorter to read; a UUID uses the familiar 36-character hex form with dashes.
Are these identifiers unique?: Yes. v4 and ULID carry 122 and 80 random bits respectively, and v7 carries 74 random bits plus a millisecond timestamp, so collisions are practically impossible at normal application volumes.